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Wide Skis As a Potential Knee Injury Risk Factor in Alpine Skiing

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Wide Skis As a Potential Knee Injury Risk Factor in Alpine Skiing ORIGINAL RESEARCH published: 18 February 2020 doi: 10.3389/fspor.2020.00007 Wide Skis As a Potential Knee Injury Risk Factor in Alpine Skiing Martin Zorko 1, Bojan Nemec 2, Zlatko Matjaciˇ c´ 3, Andrej Olenšek 3, Katja Tomazin 4 and Matej Supej 4* 1 Clinical Institute of Occupational, Traffic and Sports Medicine, University Medical Centre Ljubljana, Ljubljana, Slovenia, 2 Department for Automatics, Biocybernetics and Robotics, Jožef Štefan Institute, Ljubljana, Slovenia, 3 Research and Development Unit, University Rehabilitation Institute, Ljubljana, Slovenia, 4 Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia Alpine skis with wider waist widths have recently become more popular. With such skis, the contact point of the ground reaction force during ski turns is displaced more medially from beneath the sole of the outer ski, which may present an increased risk of injury. The aim of this study was to investigate knee joint kinetics, kinematics, and lower limb muscle activation as a function of changes of the ski waist width in a laboratory setting. A custom skiing simulator was constructed to enable simulation of different ski waist widths in a quasi-static ski turn position. An optical system was used for capturing knee joint kinematics of the outer leg, whereas a force plate was used to determine the ground reaction force vector. The combination of both systems enabled values for Edited by: external torques acting on the knee joint to be calculated, whereas electromyographic Josef Kroell, measurements enabled an analysis of knee flexor muscle activation. With respect to the University of Salzburg, Austria outer ski, the knee joint external torques were independent of ski waist width, whereas Reviewed by: Peter A. Federolf, knee joint external rotation and biceps femoris activation increased significantly with the University of Innsbruck, Austria increase of the ski waist width. Skier muscle and kinematics adaptation most probably Matthias Gilgien, Norwegian School of Sport took place to diminish the external knee joint torque changes when the waist width of the Sciences, Norway ski was increased. The laboratory results suggest that using skis with large waist widths *Correspondence: on hard, frozen surfaces may change the load of knee joint surfaces. However, future Matej Supej research is needed to clarify if this may result in the increased risk of knee injury. [email protected] Keywords: 3D kinematics, simulation, biomechanics, electromyography, injury prevention, kinetics, ski geometry Specialty section: This article was submitted to Sports Science, Technology and INTRODUCTION Engineering, a section of the journal Alpine skiing is a demanding sensory motor task with respect to maintaining balance and Frontiers in Sports and Active Living counteracting high external forces acting on the human body. It is well-documented that Received: 09 April 2019 recreational alpine skiing is associated with high injury rates ranging from 2.4 to 7.0 injuries per Accepted: 14 January 2020 1,000 activity days (Hebert-Losier and Holmberg, 2013). Such injury rates are several times higher Published: 18 February 2020 in competitive skiing compared with recreational skiing (Haaland et al., 2016). In addition to Citation: frequent acute injuries, overuse injuries are also common (Hildebrandt and Raschner, 2013; Sporri Zorko M, Nemec B, Matjaciˇ c´ Z, et al., 2015, 2016; Supej et al., 2017). The knee joint is the most frequently injured body part in both Olenšek A, Tomazin K and Supej M (2020) Wide Skis As a Potential Knee recreational and competitive skiing (Brucker et al., 2014; Haaland et al., 2016). More specifically, Injury Risk Factor in Alpine Skiing. the outer knee in the ski turn has been reported to be more prone to acute injury compared with Front. Sports Act. Living 2:7. the inner one (Urabe et al., 2002). The relationships between sudden unexpected events and/or loss doi: 10.3389/fspor.2020.00007 of balance accompanied by undesirable lower limb/knee movements while skiing and acute knee Frontiers in Sports and Active Living | www.frontiersin.org 1 February 2020 | Volume 2 | Article 7 Zorko et al. Wide Skis and Knee Injury FIGURE 1 | In a ski turn on hard frozen snow, the contact point of the ground reaction force (GRF) of the outside ski is shifted more medially with a wide ski (right: dw) than with a narrow one (left: dn). injuries have been well-established (Bere et al., 2011; Shea et al., 2014). However, the influence of ski equipment on chronic degenerative knee joint conditions is not yet clear. Human gait analysis studies have proven that even small FIGURE 2 | Skiing simulator placed on the force plate. The platform of the changes in knee joint alignment in the frontal plane, such as simulator was able to freely rotate around the sagittal axis. Two extremes of varus or valgus deformity, can substantially change the loading of the four possible ski width positions are represented (W0 represents the different joint compartments and hasten degenerative processes position of the sagittal axis beneath the middle of the sole, and W120 of the joint (Sharma et al., 2001; Levine and Bosco, 2007). In represents the simulation of waist width of 120 mm). addition, it has been shown that the human body tends to adapt to changes in body segment malalignment and asymmetrical loading of knee joint compartments (Mündermann et al., 2005). Nowadays, skis with very wide waist width on frozen compact been demonstrated (Zorko et al., 2015), the influence of ski waist snow are commonly used, although they were initially designed width on knee loading remains uninvestigated. for “soft-snow” conditions, that is, powder and/or off-piste Therefore, the aim of the present study was to examine the skiing. A previous study demonstrated that for ski turns on a knee joint kinetics, kinematics, and lower limb muscle activation hard snow base, an increase in ski waist width triggers adaptive with respect to differences in ski waist width. It was hypothesized changes of the knee kinematics in frontal and transversal planes that the wider waist width of the ski has a significant impact (Zorko et al., 2015). This field study showed that knee external on knee position, external knee torque, and muscle activation. rotation increased with wider skis and that the knee joint was in The experiment was conducted in a laboratory setting with valgus/abducted position throughout the ski turn, but, somewhat the purpose of establishing more controlled conditions where controversially, the valgus was smaller with wider skis. The vibrations (Klous et al., 2010) and other influences of uneven main limitation of the study was that the degree of knee joint terrain (Federolf et al., 2009; Supej, 2013) are excluded. flexion while turning was uncontrolled and differed substantially between volunteers. As knee joint accessory movements (rotation and valgus/varus) are coupled with the primary movement of MATERIALS AND METHODS knee in the sagittal plane (flexion/extension) to some degree, the influence of ski waist width on the knee was somewhat unclear Measurement System and uncertain. For the purpose of the study, a specially designed computer- With respect to the outer and more loaded ski involved in controlled test device was built, enabling simulation of different the turn (Vaverka and Vodickova, 2010), the point of application ski waist widths for an outer leg in the quasi-static position of the ground reaction force (GRF) moves from beneath the of a ski turn (Figure 2). The test device comprised a movable foot in the medial direction toward the ski edge (Figure 1). plate equipped with ski bindings that allowed rotation around The greater the ski waist width, the greater the shift of GRF the sagittal axis in order to mimic the behavior of the outer will be, assuming hard snow conditions where the ski does not ski. The inclination angle was measured with an inbuilt absolute sink into the snow (Federolf et al., 2010). Without changing magnetic encoder (RLS Renishaw RM22, Ljubljana, Slovenia). knee kinematics, it can also be assumed that the alignment of The test device was placed on a force plate (Kistler 9253A11, GRF with respect to the center of the joint changes with the Kistler Group, Winterthur, Switzerland) measuring GRF vector different ski waist width and accordingly also its torque. This and its point of application. Radial force (Fr) was simulated hypothetical shifting of the GRF with respect to the center of the and measured using a special harness attached to a load joint in relation to the separate knee compartment may represent cell (S9M/2 kN, HBM GmbH, Darmstadt, Germany). Eleven a critical overload, because the magnitude of GRF reaches 1.5 to2 reflective markers were placed in the following way: six on the times the body weight, even in recreational skiing (Scheiber et al., outer leg, two on the ski boot, and three on the movable plate of 2012), and up to four times the body weight in competitive skiing the simulator (Figure 3); and they were captured by a system of (Supej et al., 2004). Although the relationship between knee joint three calibrated infrared cameras (Optitrack V120:Trio, Natural kinematics and the width of the skis during ski turns has already Point, USA). Frontiers in Sports and Active Living | www.frontiersin.org 2 February 2020 | Volume 2 | Article 7 Zorko et al. Wide Skis and Knee Injury markers and EMG electrodes were applied to the subjects (as described in Measurement System) prior to measurement. Initial measurements for surface EMG of the selected muscles during maximal isometric knee extension [maximal voluntary contraction (MVC)] were taken. For isometric measurements, participants sat in an isometric torque measuring device (own design) equipped with a strain gauge force sensor (MES, Maribor, Slovenia) set at the constant lever arm to the rotational axis of the knee.
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